U.S. Sen. Elizabeth Warren said she is remaining neutral in the Democratic primary in the 5th District congressional race, despite two mailers portraying her alongside State Sen. Katherine Clark.

Warren wrote on her Facebook page on Sunday: “We are lucky to have a number of great candidates running in the fifth congressional district. I look forward to working with whoever wins the Democratic nomination in next week's primary election. Let me be clear, I'm not endorsing any of these great candidates before Tuesday's election.”

The comments came after Women Vote!, the independent expenditure arm of the group EMILY’s List, which supports female, Democratic candidates, sent out mailers featuring Clark and Warren. EMILY’s List endorsed Clark in the 5th District congressional race and supported Warren when she ran for the U.S. Senate in 2012.

One mailer sent by Women Vote! has side by side pictures of Clark and Warren under the headline “champions for the middle class.” Another mailer shows baseball cards with pictures of Clark and Warren and the phrases “At bat for the middle class” and “representing our home team.”

Boston Magazine reporter David Bernstein wrote, “I’ve seen candidates get in a little hot water just for including a photo that happens to have another, non-endorsing politician in it. Many people who receive the mailing will assume that the politician pictured has authorized its use, which in turn suggests an endorsement. And those instances have not been anything close to this.”

Scott Ferson, a spokesman for congressional candidate and State Sen. William Brownsberger, told The Republican/MassLive.com that the mailers are clearly meant to leave the impression that Warren endorsed Clark. “It seems to me that mechanically you don’t do it unless you’re concerned about your candidate losing,” Ferson said.

Eric Hyers, a spokesman for congressional candidate and State Sen. Karen Spilka, said in a statement, "We're frankly stunned to see these kinds of misleading tactics in the final days of the campaign. We can't control how other people choose to run their campaigns but we're going to continue talking about Karen's proven track record of taking on the big banks, the insurance companies, and the entrenched special interests at the state bureaucracy to win real victories for middle class families."

A spokeswoman for EMILY’s List could not immediately be reached on Monday. Neither could a spokesman for Clark.

According to financial disclosure information compiled by the non-partisan Sunlight Foundation, Women Vote! has spent $145,000 supporting Clark. The only other 5th District candidate to get significant help from outside the state is State Rep. Carl Sciortino, who has been endorsed by several national progressive groups.